Bill Cheek - World Scanner Report

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WORLD SCANNER REPORT

A Journal of VHF-UHF Radio Technology <S Engineering
Published at

COMMtronics Engineering - PO Box 262478 - San Diego, CA 92196
Publisher/Editor: Bill Cheek a.k.a. f *Doctor Rigormortis"
Administrator: Cindy Cheek a.k.a. “Sunbunny"

Copyright © 1991-95 <AU rights reserx*J> ISSN 1861-9240
Volume 5 Number 8 $5.00

some very legitimate needs to know
what’s going on in situations where it’s
ill advised to have others privy to your
eavesdropping.

Amplifier through a rotary switch so as
to afford the capability of listening to key
areas around your perimeter. Power can
be fed by a cheap DC Adapter.

SUPERSNOOP

TRANSMITTER

~ The Saga Continues ~

A reader recently complained about our
SuperSnoop series, wondering what the
hell it had to do with scanning. Well,
this month’s installment should yield a
clue or two. Think about it.

First, we presented the SuperSnoop
microphone, so sensitive, it’s capable of
detecting the heavy breathing of a couple
of gnats making w hoopee at a distance of
73 yards. But what’s so hot about a
super sensitive microphone without an
amplifier to boost the weak signals to
speaker-playback volume?

So, last month, I laid on you the
SuperSnoop Amplifier. Together, the
SuperSnoop Microphone & SuperSnoop
Amplifier are a very potent dynamic duo
that stand on their own merits.

But what about times when you are
persona non-grata and need or want to
listen in on what’s going on? The
presence of your magnificent personage
can be distracting to the goings-on, but if
you could be remotely located and still
hear, then so much the better, right?

Take you parents, fer instance. You
might use a baby monitor to keep tabs on
Junior and Queenie as they sleep. When
they get older, the baby monitor can be
moved to the rumpus room so you can
keep tabs on how much blood is being
drawn at any given time.

Trouble is.baby monitors are never as

good as they’re cracked up to be. They
don’t sound all that good for one tiling.
The units are large and bulky and cannot
be operated from batteries. They’re
definitely not portable, nor very well
suited for clandestine and treacherous
situations. Baby monitors do not make
very good bugs for a variety of reasons.

Not that I am advocating the fine arts
and sciences of surreptitious bugging; I
most assuredly am not! But there are

Take fer instance that peephole in your
front door. It’s nice to know what’s
going on outside your door before you
open it. It’s nice to know what’s going
on all around your property before you
jump into the middle of something with
both feet. But peepholes aren’t always
available, and neither do they serve the
purpose in all instances.

My SuperSnoop series can add an
immense measure of security to your
home and family. In many instances,
just the microphone and amplifier will
suffice. You could embed several
Microphones out of sight around your
property; feed their outputs into the

But wired listening devices are not
always suited to given situations.
Sometimes, radio is ideal, and that’s
where this month’s SuperSnoop
Transmitter and a scanner enter the
picture. The output of the SuperSnoop
Amplifier can be fed to the input of the
SuperSnoop Transmitter for a superb.
high quality radio listening device!

Do NOT mistake my words here....we
are talking quality\ I’m sure a lot of you
guys have experimented with Radio
Shack’s listening device, #33-1076, the
FM Wireless Mic. Cute, but no cigar.
Poor range and low sensitivity. Eats
batteries, too.

SUPER SNOOP TRANSMITTER

[NOTES:

|l. The crystal isn't critical, but probably shouldn't be lower
than 10 MHz, nor higher than 50 MHz. Synthesizer crystals

in the 22-38 MHz range from old CB radios work great!

2. An optimum value may be as high as 1100-ohms. Use

a 2-k trimpot to determine best value.

3. An optimum value may be as low as 4000 ohms. Use
a 100-k trimpot to determine best value.

4. Ground traces and connections are shown in
heavy black lines. All grounds are interconnected.

5. RF choke should be 220-uH to 470-uH or so. 1-mHok.

6. Varactor diode is critical, but try the common

ECG/NTE 613, 614, 617, 618 first. See text. ,-

+ 9 volts

O.luF

220

Audio In

• Ground

4n ^

i

^: Note 3

§

mm

0.01-uF

NPN
2N3904
2N2222A, etc

Note 4 \

■ Ground

Antenna, 10"

- Ground

12/6/95 ~ 9:02 PM ~ Page 1

Make no bones about it, my SuperSnoop
Transmitter will knock your socks off
when you hear its quality. There is no
doubt in my mind this little puppy will
equal or exceed the quality of pro-snoop
devices! It’s unbelievable! But true!

THE SECRET UNVEILED!

First. I gave you the Microphone. It’s
eminently useful as a stand-alone device,
say with tape recorders or as a feed to an
amplifier. Now just in case you didn’t
have an amplifier handy, I gave you the
SuperSnoop Amplifier to take up the
slack. Now, we add the transmitter, for
one whopper of a listening device when
remote operations are needed. I have
been spoonfeeding you a system!

But we’re not ready for the system yet.
The Microphone was a stand-alone
project, as was the Amplifier. So, too, is
the transmitter! Never mind this month
that the Microphone and Amplifier can
drive the Transmitter. This month, the
general idea is as another stand-alone
project.

Next month. I will wrap it up for you
into a single, unitary system project.
This month, we just focus on the Super
Snoop Transmitter for whatever purpose
and use you can find for it. And there
are several, not including any audio
capabilities.

SUPERSNOOP TRANSMITTER

If you need just an oscillator , as many
scannists do. in order to test your
receiving systems with a low-power
signal, the Transmitter is just right for
you. If you don't need audio transmitting
capability, then using the schematic on
page 1, amend it as shown:

You'll note we eliminated the varactor
diode, RF choke: two 10-k resistors: and

a bit of wiring. In a word, the basic
Transmitter is super easy to build, and if
you need to transmit high quality audio,
the required “extras” are not a big deal.
The rest of this project will deal with the
Transmitter as if audio were needed, but
you needn’t get hung up on that, if all
you need is a source of RF with which to
test your receivers. In that case, build
the circuit as shown on this page, and
use a small trimmer capacitor by which
to precisely adjust the frequency if
needed. You can just ground that end of
the crystal, too, and dispense with the
trimmer capacitor, as shown by the
dotted line, if you don’t need precision
tweaking capability.

THE HEART OF IT ALL

Our transmitter is just a basic cry stal
oscillator, garden variety, nothing
special. In fact, it’s so unspecial that it’s
slicker than snake snot smeared on ice.
High quality oscillators put out only one
frequency. Ours puts out a bunch of
frequencies. More on that later.

The heart-throb of the Transmitter is, of
course, the quartz crystal, and it’s not
critical aside from maybe two tilings:

(1) Frequency should not be higher than
about 40-50 MHz, nor lower than about
8 MHz. You’ll see why in a minute.
And (2), the crystal should be of the 3 rd
Overtone type, though really, most any
“rock” will do. The neat thing about
overtone crystals is that you can salvage
‘em from junked synthesizer-type CB
radios. Any CB shop will have hundreds
of synthesizer crystals on hand, one of
which shouldn’t cost much.

The ideal crystal for this project is one
with a fundamental operating frequency 7
in the 37 MHz band, of which there are
six very common cuts available from
junked CB rigs:

JsBP T i

There are many other useful values of
crystals that can be found in junked CB
radios, so there is no need to run out and
buy sometliing special. Other useful CB
synthesizer crystals are in the ranges of
23 MHz, 41 MHz, 16 MHz, & 11 MHz.

Overtone synthesizer crystals are
optimum for this Transmitter because
they allow oscillations, not only at the
fundamental frequency of the crystal, but
also at each of at least the first eight

harmonics of the fundamental. This
usually unsavory characteristic is what
lets us use a variety of crystals, down to 8
MHz or so. (Harmonics are multiples of
the fundamental.)

Let’s suppose you used a crystal with a
fundamental of 11.500 MHz. The useful
harmonics would be: 23.0, 34.5, 46.0,
57.5, 69.0, 80.5, and 92.0 MHz, or even
higher. That’s right, the oscillator will
generate all these frequencies and maybe
even more. So wliile the fundamental
and 2 nd harmonic frequencies are not
covered by most scanners, the 3 rd and
higher harmonics are....and when your
scanner is tuned to one, there will be no
doubt in your confused mind that you’re
getting a signal. It won’t take long for
you to learn how to use those signals to
test and evaluate your scanners. And if
you feed the Transmitter with a source of
audio, it will act a lot like a baby
monitor.

THE BRAIN & NERVES

If the crystal is the heart of an oscillator,
then the varactor diode (or trimmer
capacitor) is the brain and nervous
system. Now if all you want is a
transmitter (without audio), then forget
the varactor diode and just use a trimmer
capacitor as shown on this page. Or,
don’t use one, if precision adjustment of
frequency is not necessary. With the left
side of the crystal grounded as shown by
the dotted line, the crystal will use its
internal capacitance to set a resonant
frequency (and harmonics). An external
capacitor simply allows precision setting
of the resonant frequency. It’s up to you.

The Varactor Diode is the most critical
component if you want a high quality
audio transmitter. Varactors are basically
silicon diodes, but made in a special
manner that makes them act like variable
capacitors when reverse biased. The
amount of capacitance varies according
to the level of the reverse bias voltage.
By the way, all silicon diodes exhibit a
varactor effect to some degree, but only
“real” varactors can be used for our
purpose. And even then, not just any
varactor will do, though you can
experiment cheaply enough.

Before I get into the SuperWhizBang
type of varactor that you really want,
let’s take a quick look at what can be
used for the sake of experimenting. You
might never have heard of varactor

12/6/95 ~ 9:02 PM~ The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 2

ECG/NTE Varactor Tuning Diodes

NOMINAL

DIODE

CAPACITANCE ®

VR = 4 V. 1*1 MHz

TYPICAL

TUNINQ RATIO
C2/C30 Q 1 = 1 MHz

MAX REVERSE
IREAKOOWN
VOLTAGE

MAX FORWARD
CURRENT

MAX DEVICE
DISSIPATION

MIN FIGURE

OF MERIT ®

Vr * 4 Vdc. 1 * 50 MHz

CT

Pf

TR

■VR

Vcrilt

IF

mA

'0

Want

Q

610

109

6.8

2.7

30

200

200

450

611

■Tj3||

10.0

29

30

200

280

400

612

109

12.0

2.9

30

200

280

400

613

109

220

2.9

30

200

280

350

614

33.0

3.0

30

200

280

200

NTE or
ECG
Part

No.

APPLICATION

Mummi
F tnnnl
CarrvrA If

Pour

Dtulpirto*

Minimum
Ftgun of
Martt

DlaOa

Capacrtanca

CT

Capacsaaca

Rato

Volt

nA

mW

Q

PF

617

394

FM Tuning

32

280

100 ®3 V

34 (min) ® 3 V

2.5 min

618

AM Tuning

18

50

280

ISO 0 1 V

440 (min) @ 1 V

15

tuning diodes, but they are as common as
fleas on a junkyard dog. Go to your local
semiconductor supply house and buy one
each of the following ECG or NTE part
numbers: the cost is modest.

613 614 617 618

One of these may work quite well, and if
so, your search will be neither lengthy
nor costly. I can’t attest to these
varactors because I use a more costly
commercial version that I’ll tell you
about in a minute. To my way of
thinking, if the above work, then let’s
use the KISS principle. NTE/ECG
suppliers are everywhere. Sources for
my special varactor diodes are few and
far between. The above are common and
inexpensive.

The chart at the top of this column offers
clues on what varactor diodes do and
how they function. In a word, they act
like the “trimmer capacitor” shown on
the previous page. The capacitance
varies with the reverse bias placed on the
diode. ( Varactor diodes are never
forward biased....that is, we do not want
them to conduct!)

Instead, we want to send an audio (AC)
voltage to the varactor in such a manner
that its reverse bias changes at the audio
rate. When this happens, the output
frequency of the oscillator will also
change at the same rate. Voile! FM!
Frequency Modulation - for clear, noise-
free signals that can be readily received
by common scanner receivers!

Note the trimmer capacitor used in the
drawing on the previous page? As said
before, a varactor acts like a trimmer
capacitor, except that you adjust it by
changing the reverse bias voltage on the
diode. Now understand that crystals
“like” to be grounded, but happily

tolerate some capacitance in the ground
side. The more capacitance, the better,
though. Too little, and the crystal will
not oscillate. Therefore, we can’t use
just any trimmer capacitor nor just any
varactor diode. Either one must have a
certain minimum capacitance, so our job
is to select something that will not cause
any problems with oscillation. It just so
happens that 20-pF or more capacitance
is usually sufficient to stabilize a crystal
oscillator. Looking at the above chart,
we see where ECG/NTE 610-612 fall
under this mark, so we won’t consider
them for our transmitter. However, 613,
614, 617, and 618 look pretty good.

Another important tiling about varactor
diodes is the tuning ratio. A very
narrow change of capacitance relative to
the reverse bias means a small tuning
ratio. This may not be sufficient to
frequency modulate the transmitter. So
we want a fairly large tuning ratio, as
well. Diodes 613, 614, and 617 have
tuning ratios of 2.5 to 3.0, while 618 has
a whopper 15. Were it not for the “AM
Tuning” spec. I’d say go for 618. As it
is, the large 440-pF capacitance coupled
with the AM-spec might render this one
unsuitable for our needs. Try it,
Otherwise, my gut feel for a workable
varactor diode is the 617. One of the
four might yield satisfactory results.

Hyper-abrupt Tuning Diodes

As mentioned earlier, I use a special type
of varactor tuning diode called Hyper-
Abrupt. Forgive me for not explaining it
in detail, but space begs and it gets kind
of complicated. Suffice it to say that this
diode yields performance par excellence !
That’s why I prefer the KV1503 from
Frequency Sources. The MV1401 or
ZC807 from MSI Electronics should also
work equally well, though I have not

tried those from MSI. But before you go
to these commercial suppliers, there is
one other source for the superb kind of
diode I am talking about.

You die-hard CB’ers and Freebandcrs
will know of a special tuning diode used
to extend the range of SSB clarifiers or
“sliders”. Once upon a time, known as
the “M-15 diode”, “Super Slider Diode".
“Super Tune Diode” and a variety of
oilier colloquial names, these special
diodes will serve the purpose in our
SuperSnoop Transmitter. So check your
CB/hack resources for one of these
diodes, if need be. Otherwise, contact:

Frequency Sources KV-1503 diode

16 Maple Road
Chelmsford, MA 01824
(617) 256-8101 Fax (617) 256-8227
MSI Electronics MV-1401 diode

34-32 57 th Street ZC807 diode

Woodside, NY 11377
(718) 672-6500 Fax (718) 397-0972

You should expect to pay an arm and a
leg from the above sources, but maybe
prices have dropped since I last
purchased. If you run into a roadblock
finding just the right diode, I have a
small quantity of the KV-1503 and
equivalents that I can let go for just a leg.
See the end of this article for what I can
supply.

CLOSING NOTE ON VARACTORS

Don’t let these puppies intimidate you.
I’ve explained everything you need to
know about varactor tuning diodes. Just
hook the sucker up right, if you expect it

to work.which means the anode is

grounded and the cathode (banded end)
goes to the crystal.

BIAS CIRCUIT & RF CHOKE

An audio signal of several volts is fed to
the oscillator as shown on page 1. The
audio readily passes through the RF
choke to the cathode of the varactor
where it can change the capacitance as
discussed. The RF choke isolates the RF
crystal signal from the audio circuit,
however, and is very important! A
minimum of 220-uH is required, with
470-uH or even 1-mH being just fine.
We do not want RF leaking back into the
audio circuits. Chokes block RF.

Notice the two 10-k resistors, Ra & Rb l
The top of Ra goes to the +9v DC source
while the bottom of Rb is grounded.
This means that 4.5-v is dropped across

12/6/95- 9.14 FM~ The “World Scanner Report" © 1991-95; Volume 5 , No 8; Page 3

each resistor, placing a +4.5v bias on the
cathode of the varactor diode. But
cathodes need a negative voltage to make
the diode conduct! This is what I mean
by reverse bias. It prevents the diode
from conducting, even with audio signals
as high as 9-v, peak-to-peak.

If you don’t understand this hocus-pocus,
don't worry.....just build the circuit as
shown and do not change or deviate from
the Ra/Rb/RF Choke circuit as shown.

THE REST OF THE CIRCUIT

Everything else is fairly standard and
needs no special discussion here. The
transistor is not critical, but should be
rated for operation up to 100 MHz or so.
The 2N3904 or 2N2222A are known to
work quite well in the Transmitter.

The 4.7kQ (Note 3) and 3300 (Note 2)
resistors can be somewhat critical with
respect to the output power of the
oscillator. If you want to optimize or
peak this power, then start your design
with a 100-kQ trimpot in place of the
4.7kO resistor and a 2kO trimpot in
place of the 330Q resistor. Preset them
to 4.7kO and 3300 respectively, and
later, you can adjust them for maximum
signal strength at a remote receiver.
Then replace the trimpots with fixed
resistors of the values measured after the
adjustments.

MORE TECHNICAL

The SuperSnoop Trans¬
mitter requires several
volts of audio signal on
the cathode of the
varactor diode in order
to adequately FM-
modulate the oscillator.
By and large, the “loudness” of FM
modulated signals is dependent on how
much the input signal deviates the RF
carrier. Varactor diodes are not known
for permitting wide deviations, hence the
probable need for a special diode. But
even so, the modulating signal (audio)
must be a full 1-volt or more to get any
“loudness” in the transmitter output.
Low level signals like those straight from
a microphone will not adequately
modulate the oscillator.

Range of the Transmitter is extremely
variable, depending on how you build
and adjust the unit, as well as how high
and long the antenna. Under ideal
conditions with the Transmitter mounted

on the roof of my house and a 20"
antenna. I was able to listen to sounds
around my property quite effectively over
about a 1-block radius, using just a
handheld scanner. Bear in mind that
range is not always a desirable
commodity. You don’t want the rest of
the world monitoring your “personal
bugs’, do you? Length and positioning
of the antenna is a big determinant of
range. You will want to experiment.

The SuperSnoop Transmitter is designed
for DC power from +9v. I suppose you
could use somewhat higher or lower
voltages with no ill effect, but don’t stray
too far from specification.

VARACTOR DIODES of the hyper-abrupt
type are not commonly available, but can be
purchased from COMMtronics Engineering
for $15.00 ppd. See Reference Information
at the top of page 1 for contact information.
Try the cheaper ECG/NTE 617 or 618
varactor diodes first, though.

CAVEATS

You didn’t think we’d
fail to issue a caveat
or two, did you? The
biggest one is that of
bugging, which is
probably illegal as
hell. My SuperSnoop
Transmitter and related projects are not
presented with the idea of your using
them as “bugs”, though if miniaturized
and concealed, they might well make
better bugs than what the pro’s use.
Instead, these projects are specified to be
for testing and evaluating your scanners,
and perhaps for use as high quality baby
monitors, peripheral property monitors,
and legitimate tilings like that. If you
are into doing bugs, do them at your own
risk with the under-standing that if
you’re caught, you could face
incarceration and/or stiff fines.

The device could also be illegal in the
sense of violating FCC rules. Normally,
it should not be if the input power is kept
under 100-mW and if the antenna is kept
short to 10" or less. Still, I am not a
lawyer and I can’t tell you what is legal
or illegal. You and your attorney (or a
judge and jury will have to determine
that unique aspect. I just warned you
that this puppy could be illegal
depending on how and where it is used.
Use common sense and discretion with
these devices to keep out of the slammer.

NEXT MONTH? ■»

Next month, we will tie all three
SuperSnoop circuits together into one
powerhouse of a wicked little device.
Meanwhile, I urge you to build and test
these circuits independently as separate
devices. The practice of building the
separate devices for their separate uses
will pave the way for my integrated
system to come next month. You can
then connect them together for an idea of
what my total system will be like. But
for now, each circuit can have unique
little uses as independent devices.

Like the Transmitter, for instance. You
can use it as a “repeater” by feeding the
audio from a radio, hi-fi, or base scanner
into the input. Then, as you work in the
yard or around the house, just carry a
handheld scanner strapped to your waist
with an earphone to enjoy your program
source while you’re on the move.

MEMORY RETENTION CIRCUIT
FOR THE PRO-2004/5/6
EXPLAINED!

ED NOTE: This is a rehash of and take-
off from a similar article in V5N2.

Over the years, I have seen a number of
memory retention problems associated
with these fine scanners. You may as
well know something about the circuit
and how it works. Troubleshooting and
repair are relatively easy if you know
what to look for and how to test the
components. The circuits are simple and
the components are few.

Memory retention circuits are required
for these scanners because they use Static
Random Access Memory (SRAM) chips.
Lesser scanners use EEPROM memory
chips or on-board EEPROM inside the
CPU chip. Actually, EEPROM is the hot
memory chip these days because it
requires no battery or other parts to
preserve memory. The side effect is that
EEPROM chips can’t hold a lot of data
yet, and they’re expensive. Megamemory
scanners still use SRAM that requires a
constant voltage for “keep alive”.

This “keep alive” voltage has to be
present at all times, whether the scanner
in ON or OFF and whether it is
connected to power or not. The method
by which this is accomplished is reliable,
effective, simple, and inexpensive.

This discussion will use the PRO-2006
as a model, but the circuits for the PRO-

12/6/95-9.02 p\f~ The “World Scanner Report" © 1991-95; Volume 5 , No 8; Page 4

• 2004 and 2005 arc all the same. The
circuits for the PRO-2035 and 2042 are
not the same, but are close enough that
this discussion may suffice for them,
too. The text of this article uses circuit
symbols for the PRO-2006, so don’t get
confused.

Memory retention circuits for these
scanners consists of a few well placed
and selected components:

Battery

Switching diode

Current limiter resistors

CMOS voltage regulator

Filter capacitors for voltage regulator

Switching transistor

Noise filter capacitors

Now for a quick explanation of how the
Memory Retention circuit works.

PRELIMINARY: Whenever the PRO-
2004/5/6 scanners are plugged into AC
or DC power, they are never fully turned
off, even if the switch is off. See the
below sketch of a typical power supply :

It can be seen how either an AC feed or
an external DC supply will provide
power to the memory circuits even if the
scanner is turned off. Therefore, the
only circuits of critical concern are those
with the purpose of retaining memory
when there is neither AC nor DC power
connected to the scanner. The large
schematic at the top of this page shows
how it is done in the PRO-2004/5/6.

Whenever AC or DC power is connected
to the scanner, Q33 produces and feeds
about +9.2v through D56 to R-247, a
current limiter for CMOS regulator,.
IC9. Obviously, this +9.2v is regulated
to +5v and fed to the CPU and SRAM.

Now let’s back up to the cathodes of D56
and D59. The +9v from the Memory
Battery feeds through D59 to meet the
+9.2v through D56, right? Well,
theoretically, yes. In actuality, no. Take
a closer look. If +9.2v from Q33 is
present on the cathodes of D56 and D59,
and if +9v is on the anode of D59, then
D59 cannot possibly conduct because it
is reverse biased ! Well, when D59
cannot conduct, then the faucet for the
Memory Battery is effectively turned off!

MEMORY RETENTION CIRCUIT FOR PRQ-2006 (and PRQ-2004/5) |

Main Receiver Board CN-3 I Logic/CPU :

fn Board

R-256

10

R-236

P-29

+5v from IC-8

HOLD
CPU +5v

The battery will sit there forever under
that circumstance, doing absolutely
nothing, all the while Q33 produces
power for the CPU.

Remember, Q33 produces +9.2 volts any
time and all the time the scanner is
powered, either by AC or DC, no matter
whether the scanner is on or off.

The story takes a turn when AC or DC
power is lost or removed from the
scanner. Q33 goes dead with no power\
IC9 would then fail to provide power to
the CPU, except for the simple diode
logic of D59 and D56! When Q33 goes
dead, D56/D59 cathodes drop to 0-v.
Cool, because the battery’s +9v is on the
anode of D59. D59, therefore, becomes
forward biased (the faucet opens) and
allows battery power to pass to R247 and
IC9, which don’t care where power
comes from! The CPU and SRAM draw
very little current in their “sleep” states,
and so the battery can maintain memory
for months, if need be.

the above diagram. The key thing is at
the base of Q29 where a voltage is
applied from IC8, the scanner’s normal
+5v regulator. IC8 turns on and off as
the scanner is turned on and off.
Therefore the base of Q29 has either +5v
or Ov, depending. Q29 cannot conduct
when the base is Ov and always conducts
when the base is at +5v.

When Q29 is off or not conducting, and
when memory power is available from
IC9, then the voltage at the collector of
Q29 through R236 is +5v. This +5v is
passed to the CPU HOLD function via
CN3, Pin 9. When Q29 is on or
conducting, then the voltage at its
collector drops to Ov, and is passed to the
CPU HOLD function in the same
fashion. Therefore, a “low” or 0-v to the
CPU HOLD pin tells it all is well and to
kick into high gear. Conversely, a “high”
or +5v on the HOLD pin tells the CPU to
drop into a deep sleep to conserve
memory and power.

“Sleep” states? Well, yes, the CPU has
one to preserve it’s internal memory
when there is no external power. It
needs only a little squirt of memory
battery power to stay ever at the ready
when power is reapplied.

This “sleep” state is triggered by the
HOLD signal that’s generated by Q29 in

The HOLD signal clearly varies with the
status of the scanner and whether it is
turned on or off. In a word, the CPU
drops into “deep sleep” when the scanner
is turned off, and when there is no power
to the scanner. Memory is preserved in
the CPU and SRAM so long as IC9
provides +5v to the CPU and SRAM.

12/6/95 ~ 9.30 pm ~ The ''World Scanner Report" © 1991-95; Volume 5 , No 8; Page 5

This article is not complete without a
brief explanation of IC9. a very special
type of +5v regulator. The S-81250HG
is based on a CMOS design with the
intent of consuming almost no extra
current for itself. Otherwise, it is a lot
like the more common 78L05 regulator
that does the same thing, except with an
overhead of 3 mA. That’s right, the
78L05 draws 3-mA of current for itself,
in addition to whatever is drawn by the
load. That 3-mA would drain a 9-v
batten' in a week, whereas the pA drain
by the CPU and SRAM and almost no
overhead drain by IC9 can feed from the
batten for months, perhaps even years.

CARE & FEEDING OF
NiCd BATTERIES IN
HANDHELD SCANNERS

This article is long overdue. The subject
comes up all the time over the networks
and around the grapevines. Listen up,
you portable scannists: I’m fixing to lay
the good words on you from the good
book on Care and Feeding of the NiCd
Batteries In Your Handheld Scanners.

First how about some easily chewed and
swallowed brass tacks facts ?

1. NiCd batteries do not have the legendary
“ memory ejfecf\ This myth was disproved
by a NASA study over ten years ago.
Forget it. Follow these “rules”, instead.

2. A NiCd cell is fully charged at 1.44 volts.
Any more than that and it could become
damaged. A safe maximum recharge point
is 1.40 volts per cell.

3. The ( nominal ) half-charge level of a NiCd
cell is 1.20 to 1.25 volts per cell. This is
the usually published rating. Its only
meaning is “half’ or median charge.

4. A NiCd cell is considered to be fully
discharged at 1.0 volts. It could become
damaged if discharged below that level.

5. The maximum safe recharge rate of a
NiCd cell is V 3 of its ampere-hour (A/li)
rating or milliampere-hour (mA/li) rating.
(This is the fast charge C3 rate)

6 . The safe trickle (maintenance) recharge
rate of a NiCd cell is '/io of its ampere-
hour rating. (A/h or mA/h). (This is the
trickle or maintenance charge CIO rate. )

7. NiCd cells may be damaged or destroyed
by excessive heat, defined as more than
mildly warm to the touch. Cold will
usually not harm a NiCd cell, but it should
not be operated below freezing.

8 . NiCd cells can self-discharge at a rate of
up to 1% per day. Periodically recharge
stored NiCd cells.

9. It is a good idea to periodically discharge
seldom used NiCd cells to 1.0-v per cell
followed by an immediate full recharge.

10. NiCd cells fare better under cycles of full
discharge-full recharge than partial
discharge/recharge.

11. Periodically check the voltage of each
cell in a pack after it has been fully
recharged. Any cell that differs by 10% or
more from the rest, is probably in the
process of failure. When one cell goes,
others soon follow. Replace dead or weak
cells to preserve the lives of the rest!

12. Manufacturer-specified rechargers do not
always fully recharge their NiCd packs.
You should check your recharger as
described in this article to ensure that it is
optimized for your seamier. If not, take
remedial measures.

13. If you use NiCd cells that differ from
specification in the scanner manual, you
will either need a different recharger or to
modify the recharge circuit in the seamier.
For instance, if you use Radio Shack’s Hi-
Capacity™ “AA” cells (#23-149) or
nickel-metal-hydroxide cells in lieu of
Radio Shack’s Standard Rechargeable
NiCds (#23-125) in RS scanners, the
standard recharger will not provide a full
charge. This defeats the purpose of
costlier lii-performance cells.

14. A NiCd pack can only recharge up to a
value that’s equal to the recharger
terminal voltage less the sum of all voltage
drops in the recharge circuit. If the
resultant voltage is less than 1.40v per
cell, then the pack cannot fully recharge.

Ok, this about sums up what it takes to
care for and feed your NiCd powered
handheld scanners. In general, the
above rules apply to all NiCds, no matter
where they’re used, but this article
focuses on the unique needs of NiCd
cells as used in handheld scanners.

The above drawing accurately depicts the
recharge circuit used in most handheld
scanners: There may be minor

differences from one scanner to the next,
but they are not substantial.

The illustration also shows simplified
versions of that circuit so you can see it
as it counts, even if you don’t read
schematics very well. It is important that
you understand the circuit so that you
can take remedial measures as needed by
your particular scanner!

A scanner’s recharge circuit is really two
circuits in one, when you consider that it
has to recharge by one path and
discharge or power the scanner by
another. The key ingredient here is the
51 pitched RECHARGE JACK.

TYPICAL RECHARGE CIRCUIT

SIMPLIFIED DISCHARGE CIRCUIT

To/Thrv

Pcwrjmct

4-o—o-W-t

+ NiCd

R «iof
Scanner

-j-W-c)

_ Pack

When the recharger plug is inserted into
this jack, it moves contact #2 so that it
can’t touch contact #3. The (-) center
lug of the plug connects with contact #1,
while the (+) shell of the plug connects
to contact #3.

This has the effect of piping the
recharger’s output direct to the Power
Jack and the rest of the scanner, and
through RL to the NiCd battery pack. In
a word, the recharger can power the
scanner and recharge the battery at the
same time. Not recommended, though]

Meat *n taters : The recharge path is
through DL & LI into the battery, and
out through L2 and RL. Simply stated,
the recharge current goes through DL,
LI, L2 and RL, and drops a voltage
across each of these components! Take
note, because this is important.

Now consider that LI and L2 are chokes
or coils, and that their resistance is
probably well below 1 -Cl, so we can
discount their effect on the circuit. LI
and L2 are there to block sharp voltage
spikes from entering the battery, but not
to affect the recharge action. That leaves
RL and DL to evaluate, and these are
very important considerations to the
proper recharging of your NiCd pack.

No matter the output of the recharger,
diode DL drops 0.6-volt off the top. RL
drops an additional voltage equal to the
current flow through it, multiplied by its
resistance. Suppose the NiCd pack is
fully charged and is drawing a trickle
charge (Rule 6) of 45-mA.

12/6/95 - 9:02 PM- The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 6

If RL is 22Q, then the volts dropped
across RL = 0.045 x 22 or 1 volt. Add
the RL-drop to the 0.6v DL-drop for a
total drop of 1.6v. Now suppose the
NiCd pack has 6-cells. Rule 2 says 1.40
x 6 = 8.40 volts. In order for the NiCds
to receive a FULL charge, the recharger
better put out 8.40 volts plus the sum of
all drops (1.60v): exactly 10 volts\ Any
less, and the NiCds will never fully
charge. Any more, and they could be
damaged or have a shortened life span.

Now don’t get excited if there is a tenth
of a volt difference, one way or the other.
That small difference is not a concern. If
more , however, there could be trouble.

What if your recharger is not up to par?
Well, you can usually fix it, but not like
you’d think. For one thing, the actual
recharger is probably ok. It’s the
recharge circuit in the scanner that needs
the fixing. But first, let’s lay the
groundwork for how to be absolutely
certain of the quality of your recharger
and recharge circuits

It all begins with a thorough
understanding of The Rules given on the
previous page. Even if you don’t
understand them, you must abide them!

The first step to assess the quality of your
recharger system is to start with a new
set of NiCd cells. If you test with an old
set, that can’t accept a full charge of
1.40-1.44v per cell, you really won’t
know if the recharger is faulty, or if the
cells are just too old and decrepit. You
can perform the simple test on a old set
of NiCds, and if they test up to a full

charge, then well and good Older cells
usually do not fully recharge, though, so
it’s best to start with a new set.

1. Charge or recharge a new NiCd pack
for at least 18-hrs to ensure that it has
charged all that it’s going to.

2. Remove the NiCd pack from the
scanner or charger and immediately
measure and record its terminal
voltage without anything connected to
it. Ideally, it will show 1.40v to 1.44v
per cell. (A 6-cell pack should be 8.4
to 8.6 volts.) If so, all is well; you can
stop here. If not, a remedy is strongly
suggested. Here’s how:

3. Measure and record the voltage of the
recharger without it connected to
anything. This is called “open
circuit” or “ no-load voltage ”. {See K
in the above drawing.)

4. Connect the recharger back to the
freshly charged NiCd pack, and again
measure and record the voltage of the
recharger. The voltage will be less
than the no-load measurement. This
is called “ voltage under load'. {See Y.
in the above drawing.)

5. Use the milliammeter function of your
meter to measure and record the
current flow. {See A in the above
drawing.) The current flow into a
fully charged NiCd pack should not
exceed one-tenth the mA/h rating of
the pack when fully charged.

NOTE: Most handheld scanners use
“AA” cells, which can have mA/li
ratings of 450 to 1000 mA/h, depending
on the brand and type of cell. Current
flow should be 45-mA for 450 mA/h

cells and 100-mA for 1000 mA/h cells. I
have seen “AA” NiCd cells in 450. 600.
650, 800, and 850 mA/li capacities.
Nickel-metal-hydride “AA” cells can go
to 1000-mA/h.

We have two important considerations
here: (1) the terminal voltage of a fully
charged pack must not exceed 1.44v per
cell, nor be appreciably less than 1.40v
per cell, and (2) the safe maintenance or
trickle charge for a fully charged pack
should be equal to x /\ 0 the mA/li rating
(CIO) of the pack. {The ”C” rating of
one cell is the rating of the entire pack.)

If the full charge pack voltage does not
meet spec per Step 2, then chances are
the charge current measured in Step 5 is
too low (less than the CIO rating). The
remedy for this is to increase the current
just enough to meet the CIO rating but
not to exceed it. To do this, the series
limiter resistor (RL) in the scanner needs
o be dropped to a lower value. So how to
calculate it?

6. First, understand that the present
NiCd pack voltage + the diode drop
{0.6v) + the RL drop {current x
resistance) = the recharger loaded
output voltage.

12/6/95-9.02 pm ~ The “World Scanner Report” © 1991-95; Volume 5, No 8; Page 7

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»

The only thing we can alter to change
the pack voltage is the resistor. So we
calculate a new value of RL as follows:

RL = Edrop + Inow where E^p is the
voltage dropped across RL and I flow is the
current through RL. To do this, we need
to know a few other things first. Lets
collect those items that we do know for a
fact. (1) desired pack voltage, (2)
desired current flow, (3) loaded output
voltage of the recharger. Let’s work
with a practical example. Suppose the
recharger undercharges a 600-ma/H pack
with 48-ma when the pack is fully
charged to 8.32 volts.

We want:

Desired pack voltage = 8.40v-8.60v
Desired trickle charge = 60-ma

We have:

Loaded recharger output = 10.5 volts
Resistor RL = 33Q
Trickle charge = 48-ma
Fully charged cell pack = 8.32 volts

We calculate:

Edrop Iflow * RL

Edrop = 48-ma x 33Q = 1,58 volts

Totaldrop Ldrop I^ldrop

Totaldrop = 1.58v + 0.6v = 2.18 volts

Net Volts to Pack = 10.5 - 2.18 = 8.32v

Yup, so far, so good. Everything checks
out to be reasonable. So now we need to
replace RL with a lower value to allow
an Inow of 60-ma. We do this by
selecting a final full recharge voltage for
the pack....let’s be conservative and
choose 8.50 volts....halfway between 8.4
and 8.6 volts. First, we assume that the
recharger loaded output voltage won’t

change and will remain at 10.5-volts.
Now follow my logic here:

If the recharger output is 10.5v and we
want 8.5 volts (E Fina i) to the cell pack,
then the sum of all drops must be 2.0
volts. The diode DL will always drop
0.60 volts so that leaves 1.40-volts for
RL. We want a trickle charge (I no w ) of
60-ma, so now we can calculate a new
value of RL:

RLftew — (Edrop) ~ (Iflow)

RL New = (1.40-v) -s- (0.060-amp)

RLncw = 23.30

Cool! Just happens that 22Q is a common
resistor value. Replace the 33Q RL in
your scanner with a 220 resistor, and
your NiCd pack should stabilize at a
higher voltage, closer to the ideal max!

There you have it....all the tools to ensure
the health and good feeding of your
NiCd batteries. Do understand the
foregoing is not an exacting science;
rather it is an iterative process where
trial and error lead to the optimum
design for your particular scanner. If
you have more than one scanner, the
results will probably differ for each! But
now you understand why manufacturers
do things the way they do....keeps things
simple...and mediocre.

ANOTHER PET PEEVE WINNER

Anonymous bv Request: Phoenix, AZ
Hi Bill & Cindy: I need one of those PerCon CD-
ROMs, so here's my attempt.

My favorite gripe on our hobby is the press and
their coverage and sometimes lack of coverage on
our hobby. (The various rags that have some
scanner coverage or only scanner coverage, I

don't read the others) They all seem to make
huge attempt to stay away from stories that are
even a little controversial. (Read Interesting I
have not seen one mention anywhere of Laura
Quarantiello's two-facing of our hobby in "Police"
Magazine. Only on the Internet Newsgroups
could you find these types of stories. This only
backs up your position of computers and our
hobby, you must own one! I think these rags
could make better attempts to cover different
subjects each month. If you read one, you've read
them all. Even the tech articles in some seem to
be sometimes almost the same from one to the
next. I won’t ramble on, you get the idea, most of
these magazines are all the same. I enjoy the WSR
a great deal. The almost totally technical format is
exactly what I like. Thanks ©

WE’RE LATE & BEHIND

But we’ll be catching up. Apologies to all those who
have been inconvenienced by the delays. A
combination of health problems and an overload of
work conspired to put us beliind. Not to worry, every
subscription is guaranteed to receive the proper
number of issues. There are two more to go for the
1995 calendar year, and we’ll be working overtime to
get them out, hopefully this month. Do NOT be
concerned by the expiration date on your mail label if
it says “11/30/95”.. ..you’ll still receive all issues.

WHAT’S NEW?

I don’t know where to begin.....Let’s start with the
Internet. We are now represented on the World Wide
Web with a “home page ” and an FTP site\

Our WWW page address is exactly as follows:
httD://ourworld.comDuserve.cQrTVhQmeDaQes/bcheek

Our FTP site can be reached with an FTP client
program or Unix shell account exactly as follows
cts. com/usr/spool/ftp/pub/bcheek

If your WWW Browser supports FTP, the address is:
f tp: //f tp. cts . com/pub/bcheek

I’ll tell you more next issue, but for now check out
these sites and let us know what needs improvement.

Mark my words, the Information Age has dawned!

12/6/95-9:57PM- The “WorldScanner Report” © 1991-95; Volume 5, No 8; Page 8

COMMtronics Engineering
“World Scanner Report”
PO Box 262478

, > San Diego, CA 92196-2478

LAST CALL: CE-232 INTERFACE ON SALE UNTIL 12/31/95

THIS ISSUE

FIRST CLASS MAIL

951023V5N08P08

F Super Snoop Transmitter - The Saga Continues!
f Information on Frequency Sources, Inc. & MSI Electronics, Inc.

F Memory Retention Circuits of PRO-2004/5/6 Explained
+ Care & Feeding of NiCd Cells in Handheld Scanners
+ Another Pet Peeve Winner Announced!

F We’re Late and Behind - but Catching Up.

+ What’s New? We’re on the Internet - Big Time /

WWW: http: / /ourworld. CompuServe. com/homepages /bcheek

FTP Client Site: cts. com/usr/spool/f tp/pub/bcheek
FTP WWW Browser Site: ftp: / /ftp. cts. com/pub/bcheek